Drawing behavior of UHMWPE films made from solution casting
Influence of solvent quality
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Abstract
Ultra-High Molecular Weight Polyethylene (UHMwPE) fibers are well known for their very high specific mechanical properties such as tensile strength and Young’s modulus. The solution spinning/solid state drawing process invented in the late 70s at DSM enables the production of these UHMwPE fibers with outstanding mechanical properties. The achievable maximum draw ratio of the UHMwPE fibers dictates their mechanical properties. One of the possible ways to improve this maximum draw ratio (λmax) is by decreasing the quality of the solvent used for its production. Modifying the solvent in the production of UHMwPE fibers might be a way to achieve higher properties. The focus of this project is mainly to study the influence of different solvents on the production of high strength UHMwPE films/fibers. Various ways were used to decrease the quality of the solvent to gel cast UHMwPE films and then the effect of this solvent quality on the drawing properties was determined. Subsequently, the molecular between the entanglements (Me) of polyethylene chains in different solvents was investigated using shear rheology. Morphological analysis (SEM, XRD) was performed to understand the topology, crystallinity, crystal thickness of the films made in different solvents. It was found that solvent quality has a significant effect on the maximum attainable draw ratio. SEM analysis was able to distinguish between drawable and undrawable UHMwPE films. However, from XRD analysis it was found that the crystal thickness is not the controlling factor for the improvement in drawability. The required difference Me of polyethylene chains in different solvents was found but it was within the experimental accuracy which made it difficult to conclude. Furthermore, preliminary study of some of the selected solvents on the production of UHMwPE fibers was performed. The drawing results proved that one to one translation from gel casting (films) to solution spinning (fibers) process is not straightforward. And also suggested that optimization of the drawing conditions of fibers can possibly lead to achieve expected maximum draw ratios.